Lasers Aid Fuel Cell Development

Could the automotive fuel cell be ready for production sooner than some people think? That seems to be the case. According to John Mendel, senior vice president, Automobile Operations, American Honda Motor Co., Honda will introduce a production version of a fuel cell vehicle in 2008. And while GM continues to use 2010 as its stated time frame for a feasible, affordable, producible automotive fuel cell, it has had its Chevrolet Sequel out on the road with non-GM people behind the wheel, indicating, at the very least, that they’re getting there.

One of the big challenges so far as fuel cells go is in actually manufacturing the fuel cell stacks, in which the bi-polar plates and membranes are, as the name implies, stacked together, so as to generate the electrons that do the work (i.e., run a motor) and to join oxygen and hydrogen on the cathode side for the exhaust: H2O. One way that these plates may be produced in high volume operations is, according to Stan Ream, Laser Technology Leader and Fuel Cell Team Leader, Edison Welding Institute (EWI; www.ewi.org; Columbus, OH), through the use of laser welding. Recent research at EWI with a 600-W, IPG Photonics (www.ipgphotonics.com; Oxford, MA) fiber laser with a near-fundamental beam has shown the ability to weld plates at speeds on the order of 500 to 1,000 mm/sec. According to Ream, the use of lasers for bipolar plate welding is common in automotive fuel cell development operations right now—but that the lasers are running at a fraction of these speeds as the operations are primarily prototyping. The objective at hand is to be able to have not only the low-cost operations required in automotive, but a high-volume throughput rate. In addition to which, it calls for what Ream describes as “very extraordinary quality,” because, he explains, there are hundreds of plates in a stack, and “a leak in any one of these components would result in the failure of the power plant.” Or, more to the point, he states: “Six sigma doesn’t cut it.”

One of the keys to laser plate welding (and realize that although the word “plate” is being used, the material in question is on the order of 100-microns thick and they are welding to generate hermetic seals) is not only the ability to have narrow kerf widths (they’re achieving a 25-micron spot and making welds 35-microns wide), but to have low distortion resulting from the welding operation (i.e., low residual stress) because when a few hundred plates are stacked up and there’s distortion, pretty soon there’s a tilted stack.

One of the challenges that is going to need to be resolved is fixturing, which Ream says “is always going to be a challenge,” and which will “pace the operation to a significant degree.” He says that due to a variety of factors—including surface tension, plasma forces, solidification rates, and thermal conductivity—the high-speed welding that they’ve developed, which has been shown to accommodate gap tolerances in an unexpectedly beneficial way, will actually make the parts somewhat easier to fixture.